first you'll have to use the forms toolbar. on this there are options, the one you'll want to use is the text form field. you can specify the type of text (or data) that is used, and the maximum length if needed (right click on the field to get to the properties). set the font and size as normal in the font format menu.
once you have your form the way u want it, dont forget to protect it - tools > protect document... then highlight the forms option and clear any section (if u have any) that u dont want locked. (dont forget to use a password or anyone can take that protection off)
try it before using just to make sure you have it how u want it.